Torque transfer in laterally engaging drive couplers exhibiting axial misalignment with driven couplers

ABSTRACT

The present invention relates to transferring torque between a first unit, which is typically a mobile machine or a robot, and a second unit, which is typically a fixed or stationary machine. The units are arranged such that a drive coupler of the first unit designed for delivering torque about a drive axis can engage the driven coupler, which belongs to the second unit and has a driven axis, along an engagement direction that is nearly perpendicular to the direction of the driven axis. A lateral displacement mechanism in provided is the first unit to achieve a first-order coaxial alignment between the drive and driven axes. Additional measures such as compliance mechanisms are provided for improving engagement, coupling and reducing the level of axial misalignment in the apparatus and methods of the invention.

FIELD OF THE INVENTION

This application is related to apparatus and methods of torque transferbetween machines whose drive and driven couplers engage laterally oralong a direction that is substantially orthogonal or perpendicular tothe driven axis of the driven coupler, and more precisely to torquetransfer in the presence of a certain amount of axial misalignmentbetween the drive and driven axes of the drive and driven couplers,respectively.

BACKGROUND ART

There are numerous mechanisms, including well-known clutch systems thatare specifically designed for transmitting torque between machines. Manyof these mechanisms and clutch systems have parts that engage, disengageand transmit torque. For various reasons, including the need forreliable transmission of torque at different angular velocities, theprior mechanisms attempt to fix and preserve axial alignment between themachines. Typically, machines achieve this by providing for mechanicalengagement between the machines along the axis about which the torque isto be transmitted. In most conventions, this is the Y-axis of theCartesian coordinate system used in the art of mechanical engineering toparameterize clutch systems and the like.

In these prior art systems, operation commences by actuating one of thetwo couplers, either the drive or the driven coupler, along the Y-axis.Such axial motion along the Y-axis usually engages gear teeth or othercoupling features arranged in the X-Z plane and belonging to the driveand driven couplers. Such solutions are often found in power takeoffs oncars, in which an operator inserts the first coupling into the othercoupling along a common axis (axially).

One example of the prior art approach is found in U.S. Pat. No.3,747,966 to Wilkes, who teaches an agricultural tractor with anexternally splined power takeoff shaft, which extends longitudinallyfrom the rear portion. A power transmission shaft having a hollow,internally splined portion at its forward end can be connected to theexternally splined power takeoff shaft. Engagement and coupling betweenthese shafts is achieved through actuation along the axis about whichtorque is transmitted.

Another example of a prior art approach to a torque-transmittingmechanism with a latching apparatus is found in U.S. Pat. No. 7,036,644to Stevenson. Here the mechanism for engaging a torque supply isembodied by a motor with a torque output, such as a wheel. The teachingsidentify many mechanisms for linear actuation of the torque-transmittingmechanism along the axis about which torque is to be transmitted.

Still another example is provided by the teachings of Nayak in U.S. Pat.No. 6,318,657, which discloses a mechanism for transmitting torque froma coupling to a tape reel while permitting easy engagement. Here, a tapecartridge is provided with reliable reel lock and motor/reel couplingmechanisms whose functions are both accomplished during a single motionof the cartridge relative to the drive motor. Once again, this is a goodexample of actuation along the axis around which torque is transmitted.

In fact, the prior art is replete with teachings addressing axialactuation in torque transmission apparatus. For select referencesteaching standard as well as several non-standard coupling designs insuch apparatus, the reader is referred to U.S. Pat. No. 4,289,414 toRecker, DE 197 14 605 A1 to Volle, U.S. Pat. No. 4,336,870 to Shea, U.S.Pat. No. 4,635,772 to Gadelius and WO 2006/082191 to Tegtmeyer.

In applications where torque transmission needs to be performed betweena mobile unit moving laterally with respect to a stationary unit, ormany such stationary units, the typical prior art approach is oftentimesnot practicable. Specifically, when the mobile unit is a robot thatmoves laterally from station to station to transfer torque to machinerymounted at each station, traditional methods of torque transfer are notwell suited. Under these conditions repeatable and reliable axialactuation is difficult to perform.

An exemplary teaching showing how to adapt traditional torque transferapparatus and methods under these circumstances is found in U.S.Published Application 2012/01522877 Tadayon. Among many aspects, thisreference teaches a robot for solar farms where such torque transmissionto a stationary unit, e.g., a stationary unit bearing a solar tracker,is required. In one case torque transfer is accomplished by a rack andpinion mechanism. In another case the transmission of torque from therobot to the tracker is performed with the aid of a mechanism called a“tilt arm” that produces motion along the axis about which torque is tobe transmitted.

In view of the above teachings new solutions to torque transfer betweenmobile units, e.g., robots, traveling laterally with respect tostationary units, e.g., docking stations, are needed.

OBJECTS OF THE INVENTION

In view of the prior art limitations, it is an object of the inventionto provide for torque transfer between mobile and stationary units thatengage laterally or along an engagement direction that is substantiallyorthogonal to the axis about which the torque is transmitted. In otherwords, it is an objective of the invention to provide for apparatus andmethods to transfer torque from one machine to another without the needto control translation along the axis around which torque is beingtransmitted.

It is another object of the invention to provide for torque transferupon lateral engagement between drive and driven couplers belonging tosuch mobile and stationary units under conditions of axial misalignmentbetween the drive and driven axes. More precisely, it is an objective toprovide for transferring torque that can accommodate misalignment of thecouplers. The design of the coupler can be such that when torque istransmitted and the couplers are misaligned, components of the contactforces push the couplers back into stable alignment.

Still other objects and advantages of the invention will become apparentupon reading the detailed description in conjunction with the drawingfigures.

SUMMARY OF THE INVENTION

Several advantageous aspects of the invention are secured by anapparatus for transferring torque between a first unit, which istypically a mobile machine or a robot, and a second unit, which istypically a fixed or stationary machine. The apparatus has a drivecoupler mounted on the first unit and designed for delivering the torquethrough rotation about a drive axis. Meanwhile, a driven coupler with adriven axis is mounted on the second unit and arranged such that it canengage with the drive coupler along an engagement direction that issubstantially orthogonal or perpendicular to the direction defined bythe driven axis. A lateral displacement mechanism is provided for movingthe drive coupler, either independently or along with the entire firstunit. In any case, the drive coupler is moved along the engagementdirection to achieve a first-order coaxial alignment between the driveaxis and the driven axis of the driven coupler. The apparatus also has atorque delivery drive, which can be embodied by a motor, for rotatingthe drive coupler about the drive axis after the first-order coaxialalignment is achieved so as to couple to the driven coupler and transferthe torque about the driven axis. In this manner, the apparatus isconfigured to engage and transfer torque between the units wheneverrequired, but typically not on a permanent basis.

The drive coupler has a first mating member and the driven coupler has acorresponding second mating member. These members are designed or shapedto exhibit a matched geometry. Specifically, their matched geometry issuch that it defines a pass-through orientation in which the firstmember passes through the second member without making physical contact.The matched geometry further defines a relative coupling orientation inwhich the first member couples to the second member.

In preferred embodiments of the apparatus, a compliance mechanism isprovided to adapt to the first-order coaxial alignment, i.e., the levelof misalignment or the lack of high-precision axial alignment betweenthe drive and driven axes while transferring torque. The compliancemechanism itself can take on many physical embodiments and it can bemounted in various locations. For example, the compliance mechanism canbe mounted in the first unit and it can be represented by a drive-sidemechanism for adapting to the axial misalignment. More precisely, it canbe embodied by one or more flexible mounting elements attaching thetorque delivery drive, e.g., the motor, to the first unit in a mannerthat supports motion of the motor and preferably translational motion.Suitable mounting elements are springs, dampers, pistons, flexiblegrommets, linear slides and the like. Alternatively or in addition, thedrive-side mechanism for adapting to the imperfect first-order coaxialalignment can be incorporated in a drive shaft that is oriented alongand turns about the drive axis to deliver the torque. Specifically, thedrive shaft can incorporate one or more flexible elements such asflexible shafts or shaft portions, compliant linkages, helicalcouplings, universal joints, gimbals, magnetic couplings and the like.

In combination or separately from the one or more compliance mechanismsoperating on the first unit, one or more compliance mechanisms can bemounted within the second unit. Once again, these can include drive-sidemechanisms for adapting to the imperfect first-order coaxial alignmentembodied by a driven shaft oriented along the driven axis andincorporating one or more flexible shaft elements such as flexibleshafts or shaft portions, compliant linkages, helical couplings,universal joints, gimbals, magnetic couplings and the like.

The first and second mating members used by the drive and drivencouplers to couple for the torque transmission process are preferablyprovided with certain structure. For example, they have engagementfeatures designed for urging the members to assume a three-dimensionallyconstrained relative engagement pose. Preferably, the engagementfeatures not only support coupling with the amount of misalignment dueto imperfect first-order coaxial alignment, but even reduce misalignmentto a second-order coaxial alignment. The engagement features can beembodied by engagement prongs, pins, protrusions and other geometricfeatures on either member. Preferably, complementary mating features,which can be embodied by recesses, slots or ridges, are provided on theother member to urge the members into the three-dimensionallyconstrained relative engagement pose that also reduces axialmisalignment. The improvement in misalignment to a second-order coaxialalignment is especially important when the first-order coaxial alignmentis so poor that it exceeds a predetermined tolerance.

In some embodiments it is advantageous to provide the drive coupler withone or more collision-mitigating features to mitigate the impact ofcollisions with the driven coupler that can occur during regularoperation. For example, when the apparatus further comprises a rail onwhich the first unit is mounted and along which it moves between anumber of second units, collisions are likely to occur. The second unitscan be embodied by docking stations or they can be machines fixed atsuch docking stations to support equipment that requires delivery oftorque from the mobile first unit to perform certain operations. Themating members on the driven shafts of the second units can becomeoriented or re-oriented in unpredictable ways during operation. As aresult, the mating member on the drive shaft of the mobile first unitcan experience many collisions in moving from one docking station toanother.

The methods of invention are designed for transferring torque betweenfirst and second units. A preferred method calls for mounting the drivecoupler with the drive axis on the first unit and mounting the drivencoupler with the driven axis on the second unit. The drive coupler isthen moved, typically along with its entire unit, along an engagementdirection that is substantially orthogonal to the orientation of thedriven axis in order to engage with the driven coupler. In this processa first-order coaxial alignment with a certain amount of axialmisalignment that is tolerable is achieved between the drive and drivenaxes. The drive coupler is rotated about the drive axis after thetolerable first-order coaxial alignment is achieved to couple to thedriven coupler and to transfer the required torque from the first to thesecond unit. The preferred method deploys first and second matingmembers on the drive and driven couplers that are designed in a matchedgeometry. Such design ensures a pass-through orientation and a relativecoupling orientation in which the mating members couple.

In an advantageous method of the invention the driven coupler ispositioned at an idle orientation relative to the drive coupler prior toengagement. Of course, since the driven coupler has no ability to rotateon its own, it is preferable that the drive coupler rotate the drivencoupler into the idle orientation after torque transfer but prior todisengagement from the driven coupler. The idle orientation shouldensure that the driven coupler remains outside a range of angularpositions or keep-out zone, quantified by a keep-out-angle, whichrepresents driven coupler orientations that will result in undesirablecollisions with the drive coupler as it approaches the driven coupler toengage along the direction of engagement.

The method further provides for adapting to the axial misalignmentbetween the drive and driven axes by any suitable means and forproviding the couplers with mating members endowed with one or moreengagement features. Preferably, the engagement features arecomplementary and when torque is applied they force the drive and drivencouplers to assume the desirable, three-dimensionally constrainedrelative engagement pose. This becomes especially important when thefirst-order coaxial alignment is poor and exceeds a certain tolerancelevel.

The details of the invention, including its preferred embodiments, arepresented in the below detailed description with reference to theappended drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1A is a partial perspective view of a portion of a first unit and aportion of a second unit equipped with drive and driven couplersaccording to the invention.

FIG. 1B is a partial perspective view of the first and second units ofFIG. 1A as their drive and driven couplers are being coupled to transfertorque between the units.

FIGS. 2A-G are plan views illustrating engagement, rotation and couplingbetween the mating members of drive and driven couplers.

FIG. 3 is a perspective view of an apparatus in which the first unit isdisplaced along a rail in accordance with the invention.

FIG. 4 is a partial isometric view of the apparatus of FIG. 3 when driveand driven couplers are in the engaged position.

FIG. 5 is a partial isometric view of the motor in the apparatus of FIG.3 and its compliance mechanisms for adapting to first-order coaxialalignment between the drive and driven axes during torque transfer.

FIG. 6 is a partial isometric view of an embodiment in which thedrive-side compliance mechanism includes a flexible shaft.

FIG. 7A-C are partial isometric views of alternative driver-sidecompliance mechanisms deployed on the drive shaft.

FIG. 7D is a partial isometric view of a driven-side compliancemechanism deployed on the driven shaft.

FIGS. 8A-B are plan views illustrating two methods of collisionavoidance.

FIGS. 9A-E is a series of isometric views of an advantageous design andmethod of engagement between mating members using engagement featuresand achieving a three-dimensionally constrained relative engagement poseand second-order coaxial alignment correction.

FIG. 10A is an isometric view showing a positive or dog clutch fromwhich complementary engagement features are derived.

FIG. 10B is a plan view of the dog gear of FIG. 10A.

FIG. 11A is an isometric view of mating members with advantageouscomplementary engagement features.

FIGS. 11B-C are plan views of the mating members of FIG. 11A.

FIG. 12 is an isometric view of another set of members deployingcomplementary engagement features according to the invention.

FIG. 13 is an isometric view of another set of members usingcomplementary engagement features according to the invention.

FIG. 14 is an isometric view of yet another set of members usingcomplementary engagement features according to the invention.

DETAILED DESCRIPTION

The figures and the following descriptions relate to preferredembodiments of the present invention by way of illustration only. Itshould be noted that alternative embodiments of the structures andmethods disclosed herein will be readily recognized as viable optionsthat can be employed without departing from the principles of theclaimed invention.

Reference will now be made to several embodiments of the presentinvention, examples of which are illustrated in the accompanyingfigures. Similar or like reference numbers are used to indicate similaror like functionality wherever practicable. The figures depictembodiments of the present invention for purposes of illustration only.

The present invention will be best understood by first reviewing anapparatus 100 for transferring torque between a first unit 102 and asecond unit 104 as shown in the partial perspective view of FIG. 1A.First unit 102 is a mobile machine only partially shown in the drawingfigure. Second unit 104 is also a machine only partially shown, butunlike machine 102, machine 104 is fixed or stationary.

To better describe the invention and especially the relationship betweenunits 102, 104 a coordinate system 106 is used to parameterize theenvironment. Although, as any person skilled in the art will realize,any suitable coordinates can be used, we adopt herein a right-handedCartesian system with coordinate axes (X,Y,Z) oriented as shown in whichthe X-Y plane is substantially horizontal and the Z-axis issubstantially vertical. In this convention, movement or displacement ofmobile machine 102 is along the X-axis in either the positive ornegative direction.

Mobile machine 102 has a drive coupler 108 mounted to its chassis 110.Drive coupler 108 has a drive axis 112 designated with adashed-and-dotted line. Furthermore, drive coupler 108 also has a torquedelivery drive 114, in the present case embodied by a motor that has adrive shaft 116 oriented along drive axis 112. Motor 114 is designed togenerate a delivered torque τ_(D) by rotating drive shaft 116 aboutdrive axis 112.

To assist in the delivery of torque τ_(D), drive coupler 108 has a firstmating member 118 at the distal end of drive shaft 116. Mating member118 can be designed in many ways and it can conform to variousgeometries. In the present embodiment, mating member 118 is a simpleT-bar.

Meanwhile, a driven coupler 120, i.e., the coupler that is to be drivenby drive coupler 108, is mounted on a chassis 122 belonging tostationary machine 104. Driven coupler 120 has a driven shaft 124 thatextends along a driven axis 126 indicated with adashed-and-double-dotted line. Coupler 120 is arranged such that it canengage with drive coupler 108 as the latter moves along an engagementdirection 128 indicated by the corresponding arrow. In coordinate system106 defined herein, engagement direction 128 is along the X-axis.

It is noted that engagement direction 128 is close to and preferablyorthogonal or perpendicular to the direction defined by driven axis 126.Thus, according to the invention, drive and driven couplers 108, 120 aredesigned to engage laterally along engagement direction 128 rather thanaxially (along axis 112 or axis 126 as is typical for various types ofclutch and torque transfer mechanisms).

To assist in engagement, proper rotation and coupling with mating member118 of drive coupler 108, driven shaft 124 has a second mating member130 at its distal end. Here, second mating member 130 is chosen to be ayoke with two engagement features in the form of pins or prongs 132A,132B. Initially, yoke 130 is oriented such that prongs 132A, 132B arealigned almost vertically. This alignment of prongs 132A, 132B is alsoalong the Z-axis of coordinate system 106, which is almost perpendicularto the engagement direction 128 (i.e., the horizontal X-axis ofcoordinate system 106).

Mobile machine 102 has a lateral displacement mechanism 134 forpropelling or moving it along engagement direction 128. It is importantto note that lateral displacement mechanism 134 can be embodied by anysuitable mechanical arrangement capable of ensuring that drive coupler108 is reliably displaced or moved along engagement direction 128 orparallel to the X-axis in coordinate system 106 as defined herein. Inthis case, and indeed in many practical embodiments, entire mobilemachine 102 is moved for this purpose. Of course, this is not alwaysrequired, as will be appreciated by a skilled artisan.

In the present embodiment, an exemplary lateral displacement mechanism134 includes a control unit 136 and a sprocket wheel or pinion 138 thatis constrained to move along a fixed rail 140. In fact, a person skilledin the art will recognize the arrangement to be similar to arack-and-pinion mechanism. Rail 140 is composed of a series ofmechanical links and extends parallel to the X-axis. By turning pinion138, control unit 136 effectuates the requisite displacement to movedrive coupler 108 along engagement direction 128 to driven coupler 120mounted on stationary machine 104.

Control unit 136 is designed to turn pinion 138 until first matingmember 118 embodied by the T-bar is aligned with second mating member130 embodied by the yoke. More precisely still, T-bar 118 is moved untildrive axis 112 along which it extends achieves a first-order coaxialalignment with driven axis 126 along which yoke 130 extends. First-ordercoaxial alignment between drive and driven axes 112, 126 should keepaxial misalignment below a certain tolerance and thus enable reliabletransmission of torque. More specific metrics of tolerance andacceptable amount of axial misalignment between axes 112, 126 will bediscussed in more detail below.

The location of T-bar 118 at the time when first-order coaxial alignmentis established and the horizontal orientation (i.e., substantially alongthe X-axis) of T-bar 118 at this moment are shown in long-dashed lines.Note that first-order coaxial alignment can be ascertained by anysuitable sensor (not shown) or features, or by knowing the position ofpinion 138 along rack 140. The operation of requisite position sensorsand associated techniques are well known to those skilled in the art.

In the present embodiment, a permanent magnet is fixed on stationarymachine 104 and a linear position sensor is mounted on mobile machine102. The changing magnetic flux registered by the linear position sensoris used to align drive and driven axes 112, 126 to first-order coaxialalignment. Alternatively, an encoder in control unit 136 on the drivemotor that turns pinion 138 can be deployed to aid in alignment. Theencoder counts the number of revolutions of pinion 138. Based on theencoder's count, control unit 136 knows the approximate location ofmobile machine 102 along rail 140. Now, since the location of stationarymachine 104 along rail 140 is known as well, the encoder can thus beused for first-order coaxial alignment of axes 112, 126. Although eitheralignment strategy can be implemented on its own, a more robust approachcombines both of them.

After first-order coaxial alignment between axes 112, 126 is achieved,T-bar 118 is rotated by motor 114, as indicated by arrows R.Specifically, T-bar 118 is rotated about drive axis 112 until it reachesa relative coupled orientation with respect to yoke 130 as shown inshort-dashed lines.

To understand the transfer of torque between machines 102, 104 ofapparatus 100 once T-bar 118 is coupled to yoke 130 in the coupledorientation, we refer to the partial perspective view of apparatus 100afforded by FIG. 1B. Here drive and driven axes 112, 126 are shownalready aligned within the tolerance prescribed by first-order coaxialalignment. For simplicity, axes 112, 126 in this state are almostcollinear with the Y-axis of coordinate system 106. The tolerance andthe amount of axial misalignment are too small to show in FIG. 1B, andwill be addressed in more detail below.

When a coupled state between T-bar 118 and yoke 130 is thus achieved,the transfer of delivered torque τ_(D) produced by motor 114 to prongs132A, 132B of yoke 130 can commence. Of course, in the process of torquetransfer yoke 130 will react with an opposing torque τ_(O) acting onT-bar 118. It is noted that apparatus 100 is configured to engage andtransfer torque τ_(D) between machines 102, 104 whenever required, buttypically not on a permanent basis. In other words, after transferringtorque τ_(D) for a certain amount of time, T-bar 118 and yoke 130 aredisengaged and machine 102 is further displaced along direction 128.

We now turn to FIGS. 2A-G to study the engagement, rotation and couplingof T-bar 118 with yoke 130 under the condition of first-order coaxialalignment between drive and driven axes 112, 126. FIG. 2A is a plan viewillustrating T-bar 118 approaching yoke 130 laterally along engagementdirection 128. As already remarked above, given the presently adoptedcoordinate system 106, direction 128 is parallel with the X-axis.Meanwhile, the Y-axis of coordinate system 106 is pointing into the pagein FIG. 2A, as indicated. For better visualization, drive axis 112,about which T-bar 118 is configured to rotate, also points into thepage. In contrast, driven axis 126, about which yoke 130 is configuredto rotate, points out of the page. Of course, a person skilled in theart will realize that other definitions can be adopted depending onspecific set-ups and sign conventions.

It is preferable that before engagement, yoke 130 be oriented such thatprongs 132A, 132B are aligned with one another along the Z-axis, asshown in FIG. 2A. If yoke 130 were oriented with its prongs 132A, 132Bgenerally aligned with one another along the X-axis, then T-bar 118approaching laterally along engagement direction 128 would collide withyoke 130. Such collisions are undesirable and further provisions foravoiding them or mitigating their consequences are addressed below. Inthe meantime, the preferred orientation with prongs 132A, 132B along theZ-axis to limit potential collisions between T-bar 118 and yoke 130 willbe referred to herein as an idle or a pass-through orientation. Oneshould keep in mind, however, that the idle or pass-through orientationrelates to a relative orientation between T-bar 118, yoke 130 andengagement direction 128 rather than an absolute orientation incoordinate system 106.

Furthermore, according to the invention, first and second membersbelonging to the drive and driven couplers respectively, here embodiedby T-bar and yoke 118, 130, should always exhibit a matched geometry.Matched geometry as understood herein provides for the existence of atleast one pass-through orientation between the first and second members.Matched geometry thus means that first and second members 118, 130 alongwith all their engagement features, in this case just the surfaces ofT-bar 118 itself and prongs 132A, 132B, are designed or shaped to definethis pass-through orientation and its exact parameters. In thepass-through orientation of FIG. 2A, T-bar 118 moving along direction128 can pass through yoke 130, and more specifically between prongs132A, 132B of yoke 130, without making any physical contact with yoke130.

FIG. 2B shows T-bar 118 still generally oriented along the X-axis butnow moved along engagement direction 128 into position between prongs132A, 132B of yoke 130. Here the axial misalignment between drive anddriven axes 112, 126 is clearly visible. In particular, drive axis 112of T-bar 118 is offset with respect to driven axis 126 of yoke 130. Thisoffset produces axial misalignment ϵ below and to the left of drivenaxis 126 of yoke 130. The magnitude of axial misalignment ϵ is below atolerance δ (not shown) prescribed for first-order coaxial alignmentbetween axes 112, 126.

With axes 112, 126 aligned to within tolerance δ prescribed byfirst-order coaxial alignment, drive and driven couplers 108, 120 (seeFIG. 1B) are considered engaged. Now, motor 114 of drive coupler 108(see FIG. 1B) rotates T-bar 118 as indicated by arrows R. In the presentembodiment and from the vantage point depicted in FIG. 2B, the rotationis counter-clockwise and it results in T-bar 118 rotating about driveaxis 112.

FIG. 2C shows T-bar 118 rotated into an orientation in which its topsurface 118A has established contact with prong 132B of yoke 130. Atthis point, further rotation of T-bar 118 about drive axis 112 willforce bottom surface 118B to establish contact with prong 132A. FIG. 2Dshows T-bar 118 rotated by motor 114 (see FIG. 1B) into an orientationin which its bottom surface 118B has established contact with prong132A. Note that because of the already established contact between topsurface 118A and prong 132B yoke 130 may rotate slightly in thecounter-clockwise direction during this process.

It should be remarked, that since this embodiment does not deploy acompliance mechanism, the effects of sliding of T-bar 118 against theprongs of yoke 130 have to be taken into consideration. The sliding ofT-bar 118 against prongs 132A, 132B during the part of the process shownin FIGS. 2C-D will increase wear and the uneven force on yoke 130 willresult in high bending stress and could potentially even cause prongs132A, 132B to slip off of T-bar 118. In conditions where these adverseeffects are unacceptable (especially in cases of decoupling ordisengagement due to slip off), a compliance mechanism and appropriateengagement features should be used to force T-bar 118 to center itselfas much as possible to yoke 130. Suitable compliance mechanisms andengagement features are addressed further below.

The relative orientation of T-bar 118 and yoke 130 shown in FIG. 2D is arelative coupling orientation. It is the matched geometry that definesthe relative coupling orientation in which the first member couples tothe second member. In the coupled state torque can be transferred.

In the present embodiment, coupling orientation is achieved when firstmember represented by T-bar 118 is coupled to second member representedby yoke 130. More precisely, bearing top and bottom surfaces 118A, 118Bof T-bar 118 and prongs 132B, 132A of yoke 130 are coupled,respectively. Note that without a compliance mechanism it is possiblethat the bearing surfaces 118A, 118B of T-bar 118 could couple torespective prongs 132B, 132A separately for one half of each rotationcycle. This can further exacerbate the adverse effects mentioned aboveand may indicate the need for deployment of a compliance mechanism inaccordance with the invention.

FIG. 2E shows the result of application of a delivered torque τ_(D)provided by motor 114 about drive axis 112 via T-bar 118 to yoke 130while in the coupled state. In this drawing, T-bar 118 and yoke 130 havealready rotated by about 120° counter-clockwise from their coupled stateshown in FIG. 2D.

In response to delivered torque τ_(D), top surface 118A applies a normalforce to prong 132B and bottom surface 118B applies a normal force toprong 132A. Consequently, prongs 132A, 132B of yoke 130 generate normalreaction forces F_(RA) and F_(RB) as shown. Given the geometry of yoke130 and the location of driven axis 126, these forces represent opposingtorque τ_(O) of driven coupler 120 (see FIG. 1B). By rotating againstreaction forces F_(BA), F_(RB) or opposing torque τ_(O), T-bar 118 thustransfers its delivered torque τ_(D) originally generated about driveaxis 112, to yoke 130 rotating about driven axis 126. When axialmisalignment between axes 112, 126 is small and both are well alignedwith the Y-axis, once can consider the torque transfer to be about theY-axis for all practical purposes.

In general, torque transfer in the coupled state shown in FIG. 2E ismaintained for as long as driven coupler 120 on the side of stationarymachine 104 needs the torque to perform any function (see FIG. 1B). Thefunction may be mechanical or not. For example, the rotation of shaft124 of stationary machine 104 can be used to move mechanical elements oreven generate electrical power. Depending on the application, a personskilled in the art will be familiar with requisite angular velocitiesand other parameters.

FIG. 2F illustrates the first step of disengagement performed oncetorque transfer is complete. At that point, yoke 130 is preferably leftin an orientation where its prongs 132A, 132B are once again alignedalong the Z-axis. This is the idle or pass-through orientation for yoke130 already defined above. It should be noted, however, that in someembodiments it is not necessary to return yoke 130 to its idleorientation. In other words, yoke 130 can be left in an arbitraryorientation.

In the present embodiment, once yoke 130 is put in the idle orientation,T-bar 118 is rotated clockwise, as indicated by arrows D. Clockwiserotation continues until T-bar 118 reaches a horizontal orientation(along the X-axis) representing the idle or pass-through orientationdefined previously for T-bar 118. In the horizontal orientation, T-bar118 can be fully disengaged.

FIG. 2G illustrates this step of completing the disengagement. It isachieved by continued motion of T-bar 118 along the engagement direction128. Full disengagement is achieved when arbitrary rotation of T-bar 118can no longer result in any contact with yoke 130. At this point T-bar118 can be moved further along engagement direction 128 to engage withanother yoke 130′, as shown in dashed lines. Once engagement isascertained based on achievement of first-order coaxial alignmentbetween drive axis 112 and driven axis 126′ the above-described stepscan be repeated to transfer torque to yoke 130′ belonging to a differentstationary machine (not shown).

In practice, axial misalignment can be due to more factors than just theoffset between drive and driven axes 112, 126 as illustrated in the planviews of FIGS. 2A-G. Rather, besides being offset from each other, driveand driven axes 112, 126 will sometimes not be well aligned with theY-axis. In other words, in the general case axial misalignment is due tooffsets and angular alignment differences between drive and driven axes112, 126.

FIG. 3 presents in perspective view an apparatus 200 that is subject toaxial misalignment due to both offsets and angular alignmentdifferences. For convenience, parts corresponding to like parts thathave already been described above are designated by the same referencenumbers.

Apparatus 200 has a first unit 202 that is represented by a mobilerobot. Mobile robot 202 is configured to be displaced along a rail 206that is oriented generally parallel to the X-axis of coordinate system106, which is defined as in the previous embodiment. A lateraldisplacement arrangement 208 consisting of compound elements 208A, 208Bis provided for propelling mobile robot 202 along rail 206. In thepresent case, elements 208A include side mounting provisions anddisplacement means, e.g., wheels and motor or engine (not explicitlyshown). Elements 208B include front mounted guide elements, e.g.,rollers or other traction elements, and potentially another motor orengine (not explicitly shown). Of course, displacement arrangement 208can include any suitable means known to those in the art to provide forpropulsion of mobile robot 202 along rail 206.

A second unit 204 embodied by a fixed or stationary docking station, ismounted next to rail 206. Of course, many docking stations similar todocking station 204 can be positioned along rail 206. Docking station204 contains inside its protective housing 210 a mechanism (not shown)that requires periodic delivery of torque. Due to cost and complexityconsiderations, station 204 cannot be equipped with its own means forgenerating torque.

Rail 206 is provided with a marking or alignment datum 212 on rail 206next to docking station 204. Alignment datum 212 is used by lateraldisplacement arrangement 208 to determine when mobile robot 202 hasreached docking station 204. In addition, in a preferred version of thepresent embodiment, alignment datum 212 is used to indicate the positionof robot 202 on rail 206 in which first-order coaxial alignment isachieved. Of course, additional sensors such as the linear positionsensor taught above or indeed any other means of determining location ofrobot 202 with respect to docking station 204 can be deployed. In arobust system, these sensors are used in addition to alignment datum 212to reduce possibility of error and misalignment.

Mobile robot 202 is designed to deploy drive coupler 108 describedabove. Drive coupler 108 uses previously introduced parts, namely T-bar118 mounted on drive shaft 116 and driven by motor 114 to rotate aboutdrive axis 112. Motor 114 is not visible in FIG. 3 because it is locatedinside a protective housing 214 of mobile robot 202. FIG. 3, however,shows a center C of motor 114 that is on drive axis 112. Further, bodycoordinates (X_(b),Y_(b),Z_(b)) of motor 114 are also shown. Theirorigin is at center C and the body Y_(b)-axis is set collinear withdrive axis 112.

Docking station 204 deploys driven coupler 120 described above. Onceagain, driven coupler has the same parts as in the previous embodiment,namely driven shaft 124 oriented along driven axis 126 and yoke 130 withprongs 132A, 132B. The latter are for coupling with T-bar 118, which isdisplaced along engagement direction 128 (parallel with the X-axis) inthe manner described above.

FIG. 3 introduces several virtual elements for better visualization ofthe main sources of axial misalignment between drive and driven axes112, 126. First, FIG. 3 shows a virtual plane of engagement 216 thatcontains vector 128 defining the direction of engagement. In principle,since the direction of engagement as indicated here by vector 128 shouldbe orthogonal to driven axis 126, vector 128 can approach driven axis126 from any direction in virtual plane of engagement 216. In practice,of course, plane 216 is an idealization that is used here as an aid.Furthermore, note that in the present embodiment drive axis 112 is alsoorthogonal to virtual plane 216.

Next, FIG. 3 shows virtual cones 218, 220 that define the possibleangular alignment deviations of drive and driven axes 112, 126 fromtheir prescribed directions, namely parallel with the Y-axis.Specifically, the cone angles of virtual cones 218, 220 define thelargest admissible angular deviations of axes 112, 126 respectively.

During operation, mobile robot 202 is displaced along rail 206 bylateral displacement arrangement 208. Under such propulsion, robot 202approaches docking station 204 along rail 206. At the same time, T-bar118, while oriented horizontally or parallel to the X-axis, moves invirtual plane 216 along engagement direction 128. It thus approachesyoke 130 of driven coupler 120 mounted in docking station 204.

Robot 202 is stopped once T-bar 118 has reached its engagement positionwith yoke 130. The engagement position is determined from alignmentdatum 212 and can be further corroborated with any additional sensors,as indicated above. Notice that yoke 130 is in the idle or pass-throughorientation (with prongs 132A, 132B aligned along the Z-axis) which isthe preferred orientation prior to engagement with T-bar 118. As in theprevious embodiment, in the engagement position a first-order coaxialalignment between drive and driven axes 112, 126 is below a certaintolerance δ.

The first source of axial misalignment in the present embodiment is dueto an offset between axes 112, 126. This offset can be measured directlyin virtual plane 216, since it is just the distance between points whereaxes 112, 126 intersect virtual plane 216. In fact, the offset issimilar to the offset discussed in the previous embodiment and reviewedin detail with reference to FIGS. 2A-G. It can be caused by any numberof factors, including build tolerances of entire apparatus 200, wear ofwheels belonging to displacement arrangement 208, installationtolerances of rail 206 and other parts of apparatus 200 and otherwell-understood mechanical factors.

The second source of axial misalignment in the present embodiment is dueto angular alignment differences between axes 112, 126. Differently put,both axes 112, 126 can independently veer off from their intendedparallel alignment with the Y-axis of coordinate system 106. Therefore,drive axis 112 is oriented at some unknown angle within virtual cone218. Likewise, driven axis 126 is also oriented at some unknown anglewithin virtual cone 220.

When both main sources of axial misalignment (i.e., offset and angularalignment differences) are combined, the resulting first-order coaxialalignment between drive and driven axes 112, 126 can fall within arather large tolerance. This is better seen in the partial isometricview of FIG. 4, which illustrates a portion of robot 202 and dockingstation 204 when T-bar 118 and yoke 130 are in the engagement position.In fact, in this drawing figure, motor 114 is also visible as asubstantial portion of protective housing 214 is cut away.

Clearly, drive axis 112 extending along the body Y_(b)-axis and drivenaxis 126 extending along driven shaft 124 are quite misaligned. It isalso apparent, that a displacement or a rotation of either T-bar 118 oryoke 130 will be insufficient to adapt to the first-order coaxialalignment between axes 112, 126 in this situation. Some combination ofboth rotation and translation will be required to adapt to the axialmisalignment. Thus, in preferred embodiments of the invention, one ormore compliance mechanisms are provided for adapting to the first-ordercoaxial alignment, i.e., the level of axial misalignment or the lack ofhigh-precision axial alignment between drive and driven axes 112, 126.Such compliance is especially important during the time when torque isbeing transferred.

In the present case, a compliance mechanism 222 is mounted in the firstunit that is embodied by mobile robot 202. Compliance mechanism 222 is adrive-side mechanism for adapting to the axial misalignment between axes112, 126. Compliance mechanism 222 is embodied by four flexible mountingelements 224 that attach motor 114 to protective housing 214 of mobilerobot 202. Compliance mechanism 222 also includes a mounting element orstage 226 that supports motor 114 on the floor of housing 214.

Elements 224, 226 of compliance mechanism 222 support a wide range ofmotion of motor 114. In particular, elements 224, 226 supporttranslational and certain rotational motion of motor 114 within housing214. In the present embodiment mounting elements 224 are embodied bysprings and mounting element 226 is a bed or stage that is preferablysupported on a number of pistons or dampers. Other suitable mountingelements include flexible grommets, linear slides and the like. Indeed,a person skilled in the art will recognize that any mounting provisionsthat permit motor 114 to be translated and rotated, preferably in fivedegrees of freedom, are suitable.

FIG. 5 is a partial isometric view illustrating in more detail theaction of springs 224 and stage 226 that together constitute compliancemechanism 222. Specifically, FIG. 5 depicts motor 114 in its originalpose (position and orientation) when springs 224 and stage 226 are intheir equilibrium state. This condition holds prior to engagement androtation of T-bar 118 about rotation axis 112 to couple with yoke 130.Instead of showing T-bar 118 and yoke 130, however, FIG. 5 indicates thedrive and driven axes 112, 126 along which T-bar 118 and yoke 130 areoriented prior to coupling.

In order to better visualize the action of compliance mechanism 222, theaxial misalignment between drive and driven axes 112, 126 in engagementplane 216 is greatly exaggerated. The translation or offset between axes112, 126 is indicated by ϵ, as before. On the other hand, angulardeviation between axes 112, 126 is indicated by angular alignmentdifference α. Jointly, offset ϵ and angular alignment difference αdefine the first-order coaxial alignment (or axial misalignment). Note,however, that the first-order coaxial alignment needs to be less thantolerance δ, which is defined as offset ϵ and angular alignmentdifference α in this case.

Because of compliance mechanism 222, as T-bar 118 is rotated and coupleswith yoke 130 (see also FIGS. 2B-D) motor 114 can adapt to first-ordercoaxial alignment between axes 112, 126 defined by offset ϵ andmisalignment angle α. In the preferred embodiment, springs 224 and stage226 afford motor 114 the ability to move in five degrees of freedom.These include the three translational degrees of freedom and two of thethree rotational degrees of freedom available to rigid bodies.

More precisely, springs 224 and stage 226 allow motor 114 to translatealong all three axes (X,Y,Z) of coordinate system 106. The actual amountof translation is described by three-dimensional vector d, whichindicates the translation of motor 114. Once again, note that FIG. 5greatly exaggerates the amount of translation and rotation of motor 114along with its drive axis 112.

Springs 224 and stage 226 also permit motor 114 to rotate, but onlyaround two axes. To better understand the constraint on rotation ofmotor 114, we briefly review rigid body rotations, which aretraditionally described by three Euler angles (φ,θ,ψ). Specifically,Euler angles (φ,θ,ψ) describe how body axes (X_(b),Y_(b),Z_(b))originally aligned with the axes (X,Y,Z) of coordinate system 106transform after three rotations are applied in a pre-established order.FIG. 5 depicts the full set of rotations in traditional order, namely:φ, θ and then ψ. The rotation angles are defined clockwise (rather thancounter-clockwise as is more common) for reasons of visualization. Themagnitudes of Euler angles (φ,θ,ψ) define rotation of body axes(X_(b),Y_(b),Z_(b)) in the above-defined order. A skilled artisan willbe well versed in rotation conventions and alternative descriptionsthereof.

Angular alignment of axes 112, 126 requires only two rotations.Depending on the convention, these can be two of three Euler rotationsor rotations by the polar and azimuthal angles. Specifically, with tworotations drive axis 112, which is fixed in body coordinates of motor114 and collinear with body axis Y_(b), can be brought into alignmentwith driven axis 126. This is seen by examining the rotation of bodyaxis Y_(b) by first two Euler angles (φ,θ) as shown in FIG. 5. Rotationof body axis Y_(b) by first Euler angle φ to once-rotated body axisY′_(b) leaves its orientation unchanged while axes X_(b) and Z_(b) arerotated by first Euler angle φ. Next rotation of once-rotated body axisY′_(b) by angle θ to twice-rotated body axis Y″_(b) accomplishes thedesired alignment. (In accordance with convention, the primes are usedto indicate the number of rotations performed.) Thus, after rotations byrotation angles (φ,θ) drive axis 112 is in the twice-rotated statedenoted by 112″ and is aligned with driven axis 126.

Thus, translation by vector d and rotation by Euler angles (φ,θ) permitthe adaptation of the drive-side to the first-order coaxial alignment.Any rotations of motor 114 beyond those required for adapting to angularalignment difference α, should not be permitted by compliance mechanism222. In particular, no rotation of motor about drive axis 112″ should bepermitted, since this is the axis about which torque is to betransmitted. The combination of springs 224 and stage 226 should bedesigned to accomplish this objective. If required, stage 226 mayinclude an optional locking mechanism on its piston elements to preventany additional rotations and/or translations after adaptation tofirst-order coaxial alignment due to offset ϵ and angular alignmentdifference α.

It should also be stressed that in the present embodiment, driven axis126 stays rigid during the entire adaptation process. In other words, asT-bar 118 is rotating about drive axis 112 and interacting with yoke130, and while compliance mechanism 222 responds on the drive side byallowing motor 114 to be displaced by vector d and rotated by rotationangles (φ,θ), driven axis 126 stays fixed. Differently put, nomechanical compliance is provided on the side of driven coupler 120 (seeFIG. 3) or the driven side in the present embodiment. Of course, inother embodiments compliance can be deployed on both drive and drivensides or on driven side only.

The adaptation to first-order coaxial alignment or the axialmisalignment completes the coupling process between T-bar 118 and yoke130 is complete. In other words, drive axis 112 is located andorientated as indicated by 112″ before the transfer of torque commences.The remainder of the operation including torque transfer anddisengagement proceeds as previously described.

FIG. 6 is a partial isometric view of drive coupler 108 and drivencoupler 120 in the coupled state. This drawing figure illustratesanother compliance mechanism 300 on the drive side for adapting toimperfect first-order coaxial alignment between drive and driven axes112, 126. More precisely, compliance mechanism 300 is embodied here by aflexible shaft element incorporated directly into drive shaft 116.

Preferably, the material of flexible shaft element 300 is selected toexhibit a high degree of flexural deformation but a low degree oftorsional deformation. Thus, element 300 should support some adaptationto offset ϵ and limited adaptation to angular alignment difference α(i.e., some compliance to rotation by rotation angles (φ,θ). Element 300should however be entirely non-deformable under torsion about drive axis112 in order to support efficient torque transfer.

Given these requirements, a person skilled in the art will realize thatexemplary materials suitable for deployment as the compliant element 300include a flexible shaft, universal joints, or helical coupling. Inaddition, a skilled artisan will recognize that it is even possible toreplace entire drive shaft 116 by a single flexible drive shaft made ofsteel (e.g., braided steel). The flexible shaft can be mated to rigidelements by crimping, soldering or welding. Furthermore, althoughcompliance mechanism 300 can be used by itself, as illustrated in FIG.6, it can also be used in combination with compliance mechanism 222, orindeed in combination with other compliance mechanisms described furtherbelow.

FIGS. 7A-C are partial isometric views of alternative drive-sidecompliance mechanisms deployed on drive shaft 116. FIG. 7A depicts shaft116 equipped with a compliant linkage 302. In some applications a singlelinkage 302 may be sufficient to adapt to first-order coaxial alignment.In other applications, two or even more linkages may need to be used.

FIG. 7B illustrates the use of a helical coupling 304 as the driver-sidecompliance mechanism on drive shaft 116. As will be appreciated by thoseskilled in the art, the length of helical coupling 304 should be chosenbased on tolerance δ.

FIG. 7C shows the use of a universal joint 306 to adapt to axialmisalignment. Again, depending on tolerance δ, two or more universaljoints may be required on drive shaft 116 to adapt to first-ordercoaxial alignment. Of course, in any of these embodiments other elementssuch as gimbals or magnetic couplings can be used as alternative oradditional compliance mechanisms. Persons skilled in the art willrecognize that they would be incorporated into drive shaft 116 in thesame manner as the compliance mechanisms already shown.

In combination or separately from the one or more compliance mechanismsoperating on the drive side, one or more compliance mechanisms can bemounted within the second unit or on the driven side. The driven sidecompliance mechanisms can include analogous mechanisms to those used onthe drive side for adapting to the imperfect first-order coaxialalignment.

FIG. 7D is a partial isometric view of a driven-side compliancemechanism embodied by driven shaft 124 oriented along driven axis 126and incorporating a compliant linkage 308. However, it will beunderstood by those skilled in the art, that alternatives such asflexible shafts or shaft portions, helical couplings, universal joints,gimbals, magnetic couplings and the like can be used in driven shaft124. In fact, the shafts on the drive side and on the driven side candeploy any compliance mechanism from the same group of elements alreadylisted or from any group of analogous elements.

The compliance mechanism itself can take on many physical embodimentsand it can be mounted in various locations. For example, it can beembodied by spring-mounted suspensions and other compliance mechanismsattached to driven-side elements that are not explicitly shown in thepresent embodiments. As in the case of suspension of drive-side elementssuch as the motor, any spring-mounted suspensions on the driven sideshould allow for translational motion but be relatively rigid incompliance to rotations. This is especially true for rotations about thedriven axis. Such choices are made in order to support efficient torquetransfer.

There are many advantageous steps and mechanical adaptations that can beprovided in any of the basic embodiments of the invention taught above.These steps and mechanisms generally fall into three groups. The firstgroup includes collision avoidance and mitigation. The second groupincludes advantageous engagement and coupling of first and second matingmembers belonging to the drive and driven couplers, respectively. Thethird group, which is related to the second group, includes the use offeatures on the first and second mating members for improving thefirst-order coaxial alignment to a second-order coaxial alignment thatis closer to ideal coaxial alignment. A person skilled in the art willrecognize that these additional steps and adaptations can be used invarious combinations as most of them are not mutually exclusive.

FIG. 8A illustrates in a side plan view a method of collision avoidance.The method can be deployed in any of the above-described embodiments.Here, the method for collision avoidance is illustrated with T-bar 118and yoke 130 already described above.

T-bar 118 is shown moving along engagement direction 128. Yoke 130,meanwhile, is not in the preferred idle or pass-through orientation asshown, for example, in FIG. 2A. Advantageously, however, yoke 130 isstill outside a range of orientations designated by a keep-out angle β,in which a collision between T-bar 118 and yoke 130 would occur.

To avoid yoke 130 from assuming an orientation within keep-out angle β,it is advantageous that T-bar 118 rotate yoke 130 and verify that it isoutside keep-out angle β before completely disengaging after torquetransfer. This is important because the driven coupler has no ability torotate yoke 130 on its own. It is thus up to the drive coupler to eitherrotate yoke 130 into the preferred idle orientation, or, at the veryleast, leave yoke 130 in an orientation outside of keep-out angle β.

FIG. 8B illustrates in a side plan view another method of collisionavoidance. Here, T-bar 118 is inclined with respect to engagementdirection 128. Thus, as T-bar 118 approaches prong 132B of yoke 130, topsurface 118A of T-bar 118 engages with prong 132B, as shown in dashedlines. T-bar 118 then receives a torque τ_(CA) from its motor androtates counter-clockwise (not shown). In doing so, it transmits a forceto yoke 130 via prong 132B. As a result, yoke 130 is pushed out of therange of orientations delimited by keep-out angle β. The correspondingrotation of yoke 130 is designated by arrow CA and the yoke'sorientation after being pushed out beyond keep-out angle β is indicatedin dashed lines.

Having removed yoke 130 from the range of orientations defined bykeep-out angle β, T-bar 118 can be re-oriented to parallel with theX-axis. It then moves to engage, couple and transfer its regular drivetorque τ_(D), as described above. Once it completes the transfer, T-bar118 can either leave yoke 130 in its original pose within keep-out angleβ or return it to the preferred idle or pass-though orientation to allowengagement without the described collision-avoidance process.

FIGS. 9A-C illustrate in isometric views an advantageous method ofengagement and design of first and second mating members 400, 402 on thedrive and driven couplers, respectively. Members 400, 402 are providedwith certain structure to mitigate the effects of collisions and toimprove coaxial alignment between drive and driven axes 404, 406.

FIG. 9A shows member 400 mounted on a drive shaft 408. Member 400 hastwo engagement paddles 410A, 410B as well as a center void or cutout412. Paddles 410A, 410B have engagement features 414A, 414B on theirupper surfaces, which are visible in FIG. 9A. Features 414A, 414B areindentations produced in the upper surfaces of paddles 410A, 410B. Inaddition, paddles 410A, 410B have collision mitigating features 416A,416B in the form of rounded exterior edges.

Member 402 is mounted on a driven shaft 418 and has two round pins 420A,420B serving the role of its engagement features. Pins 420A, 420B may bestructurally reinforced to provide for additional collision mitigationon the driven side of the apparatus. It is noted that the constructionof member 402 is related to the previously described yoke 130.

Members 400, 402 are designed to engage laterally along engagementdirection 128. Member 400 is indicated in dashed lines at the initialpoint of contact with pin 420A of member 402. It is noted that thecontact generally produces a collision. We note that the adverse effectsof such collision are mitigated by the aforementioned compliancemechanism and collision mitigating features. In the present orientationof member 400, mitigating feature 416B deflects member 400 downward andunder pin 420A.

It should be noted that drive shaft 408 of member 400 is preferablycompliant in this embodiment to further promote downward or upwarddeflection of member 400. For example, drive shaft 408 can be made of acrossed steel mesh to support bending but remain rigid under theapplication of torsional stress and thus promote efficient torquetransfer.

FIG. 9B illustrates member 400 in engagement with member 402. At thispoint, a first-order coaxial alignment between drive and driven axes404, 406 is established. Notice, however, that the first-order coaxialalignment achieved in this case is not the expected or desired alignmentfor the drive and driven couplers as previously illustrated in FIG. 2C.Pins 420A, 420B are located on paddles 410A, 410B and they are pressedagainst engagement features 414A, 414B.

FIG. 9C shows member 400 commencing its counter-clockwise rotationindicated by arrow R. The rotation forces paddle 410A to disengage frompin 420A as member 400 pivots about pin 420B. The pivoting action aboutpin 420B is further supported by engagement feature 414B (not visible inFIG. 9C). The pivot axis P about which the pivoting takes place isindicated in a dashed line. At this point is becomes clear that thechoice of a compliant drive shaft 408 is advantageous as, in addition toengagement feature 414B, it further facilitates the pivoting action.

FIG. 9D illustrates rotation and loading of member 400 against pin 420B.This occurs as the force of static friction between pin 420B and feature414B of paddle 410B is be overcome by the force built up in deflecteddrive shaft 408 and whatever compliance mechanisms are being deployedbesides compliant drive shaft 408 (see above for other compliancemechanisms).

Finally, as shown in FIG. 9E, paddle 410B of member 400 slips off pin420B. Because of the presence of cutout 412, pin 420B is able to passthrough this void and member 400 is able to reach the desired engagementwith member 402. Note that engagement features 414B, 415A of member 400and engagement features 420A, 420B of member 402 also urge members 400,402 to assume a three-dimensionally constrained relative engagement poseshown in FIG. 9E. The assumption of this pose is supported by engagementfeatures 414A, 415B on the other sides of paddles 410A, 410B when member400 is rotated 180 degrees from the orientation shown. Preferably,features 415A, 415B are recesses dimensioned to engage and hold pins410A, 410B.

Another advantageous aspect of the embodiment shown in FIGS. 9A-E isthat the three-dimensionally constrained relative pose thus achievedimproves the axial alignment of drive and driven axes 404, 406.Specifically, by comparing the imperfect first-order coaxial alignmentin FIG. 9B and second-order coaxial alignment in FIG. 9E after the“flip” maneuver preformed by member 400 (the “flip” is shown in FIGS.9C-E) it is quite clear that the second-order coaxial alignment isalmost truly coaxial.

In view of the above embodiment, it is clear why it is advantageous toprovide for complementary engagement features that promote or urge thetwo mating members of the drive coupler and the driven coupler in amanner that leads to three-dimensionally constrained relativeengagement. Even more preferable are complementary engagement featuresthat lead to constrained engagement and also reduce misalignment to amore accurate second-order coaxial alignment. The latter is even moreimportant in embodiments where first-order coaxial alignment is expectedto be poor or may frequently exceed the desired tolerance δ.

As already indicated, appropriate engagement features can be embodied byrecesses, slots, ridges and the like. These can be provided on the firstmating member, the second mating member or both. In fact, there are alsoseveral advantageous geometries of complementary engagement features topromote accurate second-order coaxial alignment as well as provide forwell-constrained engagement that is relatively immune to externalforces.

FIGS. 10A-B illustrate the principle behind such advantageous designs ofcomplementary engagement features based on a dog clutch 500. FIG. 10A isan isometric view of dog clutch 500 and its two mating members 502, 504.Mating member 502 has three coupling features 506A, 506B, 506C. Member504 also has three coupling features 508A, 508B, 508C. Member 502 is thedrive member and thus engages coupling features 508A, 508B, 508C withits coupling features 506A, 506B, 506C to deliver torque.

FIG. 10B is a plan view that illustrates the forces applied to couplingfeatures 508A, 508B, 508C of member 504 by member 502 when acounter-clockwise driving torque is applied. Given that there are threeengagement points and three corresponding non-parallel drive forcevectors F1, F2, F3 that define the engagement torque the overallengagement is very stable.

Specifically, the engagement is stable because any external force isunable to break the engagement, unless it exceeds in magnitude themagnitude of a vector sum of the drive force vectors F1, F2, F3 thatcombine to directly oppose the external force. The principles behindthis stability will be familiar to those skilled in the art.

Of course, dog clutch 500 in the embodiment shown is not amenable to thepresent invention due to the requirement for lateral engagement betweenthe drive and driven couplers. However, the principle of using threeforces F1, F2, F3 in the manner depicted in FIG. 10B is directlyapplicable to couplers that can be used in the apparatus and methods ofthe instant invention.

FIG. 11A illustrates mating members 600 and 602 in an isometric view.Members 600, 602 are provided with complementary engagement features604, 606 and 608, 610, respectively, in order to establish the desiredthree points of contact and hence three drive forces F1, F2, F3. As inthe prior embodiments, engagement direction is indicated by vector 128.

FIG. 11B is a plan view illustrating the engagement of members 600, 602.The pre-engagement position of member 600 is indicated in dashed lines.

FIG. 11C is another plan view showing the coupling achieved betweenmembers 600, 602 and the three drive forces F1, F2, F3 generated betweenthem due to the complementary design of engagement features 604, 606 and608, 610. Note that, again, drive force vectors F1, F2, F3 arenon-parallel and oriented so that they can combine to resist an in-planeexternal force of any orientation.

FIG. 12 illustrates in isometric view another possible design ofcomplementary engagement features in two members 700, 702. The isometricviews afforded by FIGS. 13 and 14 illustrate two other advantageousdesigns of members 800, 802 and members 900, 902 with complementaryengagement features. Note that in the last two figures the correspondingmembers are already properly coupled and ready for torque transmission.Also note that for these last two designs, coupling the correspondingmembers results in four contact forces rather than three contact forcesof previous designs.

The apparatus and methods of invention admit of many alternativeembodiments. For example, collision-mitigation features can be deployedon the drive and driven sides as the driven side as a function ofexpected velocities and dimensions of the apparatus. The apparatus canbe deployed in indoor and outdoor environments. An appropriateapplication of the embodiment in which the mobile robot moves on a railis in the solar industry. In such applications the robot can movebetween docking stations that are solar trackers 205 (see FIG. 3) anddeliver torque to periodically adjust their orientation with respect tothe sun.

In view of the above teaching, a person skilled in the art willrecognize that the apparatus and method of invention can be embodied inmany different ways in addition to those described without departingfrom the spirit of the invention. Therefore, the scope of the inventionshould be judged in view of the appended claims and their legalequivalents.

We claim:
 1. An apparatus for transferring a torque between a mobilemachine unit with a torque delivery drive and a stationary machine unitadapted to perform certain operations upon delivery of torque to adriven shaft thereof, the apparatus comprising: a drive coupler fordelivering the torque through rotation about a drive axis, the drivecoupler being mounted on the mobile machine unit, the mobile unit havinga lateral displacement mechanism for moving the mobile unit along anengagement direction substantially orthogonal to the drive axis and thetorque delivery drive configured for rotating the drive coupler aboutthe drive axis; a driven coupler on a distal end of the driven shaft ofthe stationary machine unit, the driven shaft having a driven axis andbeing mounted on the stationary machine unit, the driven coupler beingarranged for engaging with the drive coupler along an engagementdirection substantially orthogonal to the driven axis from a disengagedposition using only movement in the engagement direction, whereinengagement of the drive coupler and driven coupler further aligns thedrive coupler and driven coupler to facilitate transmission of torquetherebetween; wherein the lateral displacement mechanism is configuredfor moving the drive coupler along the engagement direction to achieve afirst-order coaxial alignment between the drive axis and the drivenaxis; wherein the torque delivery drive is configured for rotating thedrive coupler about the drive axis after the first-order coaxialalignment is achieved to engage the drive coupler with the drivencoupler to achieve a second-order coaxial alignment between the driveaxis and the driven axis and then transfer said torque about the drivenaxis; whereby the apparatus transfers the torque from the mobile machineunit to the stationary machine unit, wherein the driven couplercomprises a pair of rounded pins spaced apart and extending parallel tothe driven axis, and the drive coupler comprises a pair of engagementpaddles with a center void therebetween, each of the pair of engagementpaddles extending distally along the drive axis and having anindentation that extends longitudinally in parallel with the drive axisalong an outer surface thereof so as to engage the pair of rounded pinsof the driven coupler upon rotation of the drive coupler when co-axiallyaligned with the driven coupler.
 2. The apparatus of claim 1, whereinthe drive coupler comprises a first mating member comprising the pair ofpaddles and the driven coupler comprises a second mating membercomprising the pair of pins, the first mating member and the secondmating member having a matched geometry defining a pass-throughorientation in which the pair of paddles of the first mating memberpasses between the spaced apart pair of pins of the second mating memberwithout physical contact to facilitate lateral displacement of the drivecoupler relative the driven coupler to achieve first order-coaxialalignment therebetween.
 3. The apparatus of claim 2, wherein the matchedgeometry further defines a relative coupling orientation in which thefirst mating member couples to the second mating member such that thepair of pins are engaged within the indentations of the pair of paddlesthereby facilitating transfer of torque from the torque delivery driveof the mobile machine unit to the driven shaft of the stationary machineunit.
 4. The apparatus of claim 1, further comprising a compliancemechanism for adapting to the first-order coaxial alignment between thedrive axis and the driven axis during coupling and transfer of torqueabout the driven axis.
 5. The apparatus of claim 4, wherein saidcompliance mechanism is mounted within the mobile machine unit andcomprises a drive-side mechanism configured for adapting to theorientation of the drive axis.
 6. The apparatus of claim 5, wherein thedrive-side mechanism configured for adapting to the orientation of thedrive axis comprises at least one flexible mounting element attachingthe torque delivery drive within the mobile machine unit and supportingmotion of the torque delivery drive with respect to the mobile machineunit.
 7. The apparatus of claim 6, wherein the flexible mounting elementis selected from the group consisting of springs, dampers, pistons,flexible grommets and linear slides.
 8. The apparatus of claim 5,wherein the drive-side mechanism configured for adapting to theorientation of the drive axis comprises a drive shaft oriented along thedrive axis and comprising at least one compliant element.
 9. Theapparatus of claim 8, wherein the compliant element is selected from thegroup consisting of flexible shafts, compliant linkages, helicalcouplings, universal joints, gimbals and magnetic couplings.
 10. Theapparatus of claim 4, wherein the compliance mechanism is mounted withinthe stationary machine unit and comprises a driven-side mechanismconfigured for adapting to the orientation of the driven axis.
 11. Theapparatus of claim 10, wherein the driven side mechanism configured foradapting to the orientation of the drive axis comprises the driven shaftoriented along the driven axis and comprising at least one compliantelement.
 12. The apparatus of claim 11, wherein the compliant element isselected from the group consisting of flexible shafts, compliantlinkages, helical couplings, universal joints, gimbals and magneticcouplings.
 13. The apparatus of claim 1, wherein the drive couplercomprises a first mating member that comprises the pair of paddles andthe driven coupler comprises a second mating member comprising the pairof pins.
 14. The apparatus of claim 13, wherein the pair of pins and theindentations of the pair of paddles are arranged for urging the firstmating member and the second mating member to assume athree-dimensionally constrained relative engagement pose in which thefirst-order coaxial alignment is adjusted to the second order coaxialalignment when the pair of pins are engaged within the indentations ofthe pair of paddles and the drive coupler is rotated.
 15. The apparatusof claim 13, wherein the pair of pins and the indentations of the pairof paddles are arranged for urging the drive coupler to assume athree-dimensionally constrained relative engagement pose when thefirst-order coaxial alignment exceeds a predetermined tolerance.
 16. Theapparatus of claim 1, wherein the drive coupler further comprises atleast one collision-mitigating feature for mitigating the impact ofcollision with the driven coupler.
 17. The apparatus of claim 1, whereinthe driven coupler further comprises at least one collision-mitigatingfeature for mitigating the impact of collision with the drive coupler,wherein the collision-mitigating feature comprises rounded exterioredges of the pair of paddles.
 18. The apparatus of claim 1, furthercomprising a rail for mounting the mobile machine unit such that themobile machine unit moves along the rail.
 19. The apparatus of claim 1,wherein the stationary machine unit is a solar tracker.
 20. An apparatusfor transferring a torque between a mobile machine unit with a torquedelivery drive and a stationary machine unit adapted to perform certainoperations upon delivery of torque to a driven shaft thereof, theapparatus comprising: a drive coupler for delivering the torque throughrotation about a drive axis, the drive coupler being mounted on themobile machine unit, the mobile unit having a lateral displacementmechanism for moving the mobile unit along an engagement directionsubstantially orthogonal to the drive axis and the torque delivery driveconfigured for rotating the drive coupler about the drive axis; a drivencoupler on a distal end of the driven shaft of the stationary machineunit, the driven shaft having a driven axis and being mounted on thestationary machine unit, the driven coupler being arranged for engagingwith the drive coupler along an engagement direction substantiallyorthogonal to the driven axis from a disengaged position using onlymovement in the engagement direction, wherein engagement of the drivecoupler and driven coupler further aligns the drive coupler and drivencoupler to facilitate transmission of torque therebetween; wherein thelateral displacement mechanism is configured for moving the drivecoupler along the engagement direction to achieve a first-order coaxialalignment between the drive axis and the driven axis; wherein the torquedelivery drive is configured for rotating the drive coupler about thedrive axis after the first-order coaxial alignment is achieved to engagethe drive coupler with the driven coupler to achieve a second-ordercoaxial alignment between the drive axis and the driven axis and thentransfer said torque about the driven axis; whereby the apparatustransfers the torque from the mobile machine unit to the stationarymachine unit, wherein the driven coupler comprises a yoke having a pairof rounded pins spaced apart and extending parallel to the driven axis,and the drive coupler comprises a pair of engagement paddles with acenter void therebetween, each of the pair of engagement paddlesextending distally along the drive axis and having an indentation alongan upper surface thereof arranged to engage the pair of rounded pins ofthe driven coupler upon rotation of the drive coupler when co-axiallyaligned with the driven coupler.